My nephew is in Juvie

My nephew is in Juvie for trying to kill his step father... I already knew this shit was gonna happen... His step father was sexually abusing him and my sister didn't do shit or care. I had called CPS so many times but nothing got done. I remember being on the phone with my nephew and him pretty much breaking and saying he wants to kill him. This sexual abuse has been going on for years. My sister loved her man more than her son... What he told me that happened to make him break was he trying to draw and his step dad came into his room and started touching between his legs. For once my nephew pushed him so he grabbed my nephews face and my nephew bit him and took his baseball bat in his room and went and beat the shit out if him with it. My sister called the police on her son and decided to press charges. Seems like he's only gonna do 8 months to a year in Juvie. He did tell why he did it but my sister said he's a pathological liar and he never touched him and shit like that. Such bullshit. She knew what was going on because when I confronted her about it a couple years ago she told me to mind my business. Then she has the nerve to get on Facebook and make a post saying some shit like "Thank you everyone for your prayers. Even after what Alan did, Jessie still loves him as his own. I hope this will be a learning experience for Alan and that he will face his consequences and come out a better person." Some shit like that! I understand she's my sister and she's family but I have never wanted to kill her more than when I read that disgusting post. I have talked to my nephew and he says he doesn't regret anything and he's actually happy in Juvie because for once in his life he feels free from his step dad... He should be out before he turns 18 but I let him know he has a home at my house when he gets out. My sister was saying she wasn't letting him back home because she can't have a "dangerous" person in her house. He calls me when he can and now it's just counting down the days until he can get out.